Nanocellulose was prepared by acid hydrolysis of microcrystalline cellulose (MCC) at different hydrobromic acid (HBr) concentrations. Polyvinyl alcohol (PVA) composite films were prepared by the reinforcement of nanocellulose into a PVA matrix at different filler loading levels and subsequent film casting. Chemical characterization of nanocelluloses was performed for the analysis of crystallinity (X c ), degree of polymerization (DP), and molecular weight (M w ). The mechanical and thermal properties of the nanocellulose reinforced PVA films were also measured for tensile strength and thermogravimetric analysis (TGA). The acid hydrolysis decreased steadily the DP and M w of MCC. The crystallinity of MCC with 1.5 M and 2.5 M HBr showed a significant increase due to the degradation of amorphous domains in cellulose. Higher crystalline cellulose showed the higher thermal stability than MCC. From X-ray diffraction (XRD) analysis, nanocellulose samples showed the higher peak intensity than MCC cases. Reduction of MCC particle by acid hydrolysis was clearly observed from scanning electron microscope (SEM) images. The tensile and thermal properties of PVA composite films were significantly improved with the increase of the nanocellulose loading.
Staff are interested in developing knowledge and skills pertinent to the psychological problems of their patients and their views reveal a consensus that the most important areas for learning are recognition of mental disorders, anxiety management, crisis intervention and pharmacological treatments for depression.
The effects of chemical modification (silane coupling) and filler loading on the fundamental properties of the bamboo fiber (BF) filled polypropylene (PP) bio-composites were investigated in this study. Mechanical properties of the PP/ BF composites, such as the tensile strength, flexural strength, and impact strength decreased as BF loading increased. However, the tensile modulus, flexural modulus, and water absorption were increased by the increase of the BF loading. The addition of aminopropyltrimethoxysilane (AS) and tetramethoxy orthosilicate (TMOS) after the alkali pretreatment for the BF increased all the tensile, flexural, impact strength, and water desorption of the resultant composites, resulting from the improved adhesion between the BF and PP matrix. This tendency was more obvious with the increase of the BF loading. The melting temperature, melting enthalpy, crystallization enthalpy, and crystallinity were decreased by the increase of BF loading and the AS and TMOS treatments. One the other hand, the crystalline temperature was increased by the addition of the BF, AS, and TMOS. Hence, AS and TMOS are considered as effectual coupling agents for the PP/BF composite systems.
Southern pine samples with different dimensions and bulk densities were impregnated with the multifunctional monomer ethyl a-hydroxymethylacrylate (EHMA) and 5 mol % of fluorinated or nonfluorinated crosslinking agent. The maximum impregnation yield ( 105% by weight) was achieved under vacuum with good improvement of water repellency.Impregnation with EHMA plus another multifunctional monomer 2-vinyl-4,4-dimethyl-2-oxazolin-5-one (vinyl azlactone ) was carried out to improve the mechanical properties of wood samples. Water repellency was also improved depending on the amount of vinyl azlactone in the monomer solution. A maximum of 41% antiswell efficiency (ASE) was obtained by impregnation with a 9 : 1 w/w mixture of EHMA and vinyl azlactone. Improvements of 38-54% in impact strength and 27-44% in compression modulus were achieved depending on the relative amount of vinyl azlactone incorporated. FT-IR and solution or solid-state NMR spectroscopy were used for chemical characterization of the polymers themselves and the wood-polymer composites.
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